Understanding of biological nitrogen fixation has advanced with impressive rapidity during the last decade. As befits a developing area of Science, these advances have uncovered information and raised questions which will have, and indeed have had, repercussions in numerous other branches of science and its applications. This 'information explosion', to use one of to-day's cant idioms, was initiated by the discovery, by a group of scientists working in the Central Research laboratories of Dupont de Nemours, U. S. A. , of a reproducibly active, cell-free enzyme preparation from a nitrogen fixing bacterium. Full credit is due to them. But subsequent developments, albeit sometimes quite as impressive, have too often been marked by that familiar disorder of a developing field of research-the scramble to publish. It is a scramble which, at its best, may represent a laudable desire to inform colleagues of the latest developments; yet which too easily develops into an undignified rush for priority, wherewith to impress one's Board of Directors or Grant-giving Institution. This, in miniature, is the tragedy of scientific research to-day: desire for credit causes research to be published in little bulletins, notes and preliminary communications, so that only those intimately involved in the field really know what is happening (and even they may well not see the forest for the trees). Those outside the field, or working in peripheral areas, may glean something of what is going on from reviews and fragments presented at meetings, but the broad pattern of development is often elusive.
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Table of Contents1 The Background.- 1.1 Introduction.- 1.2 Properties of the Enzyme System in Azotobacter.- 1.3 The Properties of the Enzyme System in Leguminous Plants.- 1.4 The Chemical Pathway.- 2 Abiological Nitrogen Fixation.- 2.1 Introduction.- 2.2 The Properties of Dinitrogen.- 2.3 Modes of Reaction of Dinitrogen.- 2.4 A Possible Mechanism for Biological N2-Fixation.- 3 Dinitrogen Complexes and Nitrogen Fixation.- 3.1 Introduction.- 3.2 Terminal-Dinitrogen Complexes.- 3.3 Bridging-Dinitrogen Complexes.- 4 Fixation by Free-Living Micro-Organisms: Enzymology.- 4.1 Introduction.- 4.2 Extraction, Purification and Properties of the Enzymes.- 4.3 Cofactors in N2 Fixation.- 4.4 Reactions Catalyzed by Nitrogenase.- 4.5 Inhibitors of N2 Fixation.- 4.6 Kinetics of N2 Fixation.- 4.7 Metabolic Schemes for N2 Fixation.- 5 Fixation By Free-Living Microbes: Physiology.- 5.1 Introduction.- 5.2 The Reductive Character of N2-Fixation.- 5.3 The Need for ATP.- 5.4 The Need for Iron and Molybdenum.- 5.5 Conclusion: Some Unresolved Problems.- 6 Physiological Chemistry of Symbiotic Nitrogen Fixation by Legumes.- 6.1 Introduction.- 6.2 The Symbiotic Association.- 6.3 Specific Mineral Requirements.- 6.4 Leghemoglobin.- 6.5 The Nitrogenase System.- 6.6 Electron Transport.- 6.7 Conclusions 236 Addendum.- 7 Physiological Chemistry of Non-Leguminous Symbiosis.- 7.1 Introduction.- 7.2 Biological Aspects of Non-Leguminous Symbiosis.- 7.3 Physiological and Biochemical Aspects of Nitrogen Fixation in True Root-Nodule Symbiosis.- 7.4 Physiological and Biochemical Aspects of Nitrogen Fixation in Superficial Root-Nodule Symbiosis.- 7.5 Physiological and Biochemical Aspects of Foliar Nitrogen Fixation.- 7.6 Physiological Ecology of N2 Fixation by Non-Legumes.- 7.7 Speculations on the Evolution of Symbiotic Nitrogen Fixation in Root-Nodule and Foliar Symbiosis of Non-Legumes.- Appendix 1 A Review of Research by Soviet Scientists on the Biochemistry of Nitrogen Fixation.- A1.1 Introduction.- A1.2 The Nitrogenase Reaction.- A1.3 Enzymes Associated with Nitrogen Fixation: Electron Transport.- A1.4 Mechanisms of the Nitrogenase Reaction and the Nature of the Active Site.- A1.5 Separation of Nitrogenase into its Component Fractions.- A1.7 Conclusion.- Appendix 2 The Acetylene Test for Nitrogenase.- A2.1 Introduction.- A2.2 Equipment.- A2.3 Gases.- A2.4 Tests of Soil, Water and Tissue Samples.- A2.5 Tests of Aerobic Micro-Organisms.- A2.6 Tests of Facultative and Obligate Anaerobes.- A2.7 Tests of Enzyme Preparations.- A2.8 Interpretation.